l8 Charles GELDERD 



The study of the posterior chamber has been very much neglected in 

 ail the groups. Ail investigators agrée that this portion is extremely com- 

 plicated and difficult to understand. They bave attributed to it a function 

 simply valvular or at the most that of a filter or sphincter. Professer Ide 

 was the first to call in question the physiological rôle given to the pyloric 

 chamber by the various investigators. Professer Ide treated only of the 

 Amphipoda and Isopoda, In the Schizopoda the pyloric chamber is much 

 more complicated, and we shall see that in the species that we hâve exa- 

 mined its chief fonction is to mix the sécrétions from the digestive glands 

 with the food stuffs reduced to a very fine pulp in the cardiac chamber. It 

 is true that the upper part of the pyloric chamber has a valvular fonction, 

 as we shall see in our anatomical descriptions. 



Cardiac chamber. 



We hâve seen from our dissections that this portion of the stomach is 

 a large cavity oval in form, occupying most of the cephalic région. It 

 extends for some distance into the thorax, fig. 3. 



The entire cavity is covered with a chitinous cuticle which is raised 

 into reliefs or plates in various places. Thèse constitute the gastric mill. 

 Thèse plates are armed with teeth and hairs of various kinds. 



We shall see that the cardiac chamber possesses three principal reliefs. 

 S, are a pair of large latéral plates, psm the superior médian pièce is un- 

 paired, fig. 3. 



We shall examine, by means of sections, each of thèse reliefs. To ob- 

 tain a correct idea of thèse pièces it is necessary to examine their sections 

 in différent directions, vertical, transverse and horizontal. 



Fig. 2, S, shows the latéral aspect of the great paired plates. 



Fig. 11, 12, 13, 14 are horizontal sections at différent levels through 

 the two chambers of the stomach. It is important to bear in mind that the 

 cuticle of the reliefs has become detached from the epithelial cells which 

 support it, under the action of the fixing solutions. Yet, we are convinced 

 that the separated cuticle is a faithful représentation of the nature of thèse 

 reliefs in the living animal. During life the empty space between the 

 cuticle and the matrix was occupied by the epithelial cells. 



We shall examine first the latéral plates. S, in the différent figures 

 which represent sections through thèse pièces. 



In fig. 11, which is a horizontal section through the dorsal part of the 



